1. Field of the Invention
This invention relates to reclosing relays which automatically reclose circuit breakers in electric power transmission and distribution systems after they have been opened by other protective relays. More specifically, it relates to a microcomputer based reclosing relay and particularly to aspects of such a relay which provide continuity of operation despite interruption in power to the relay microcomputer.
2. Background Information
Reclosing relays are commonly used to automatically reclose circuit breakers in electric power systems which have been opened by overcurrent or other protective relay action. Typically, the reclosing relay provides several reclosures at predetermined intervals in case the fault which initiated tripping of the circuit breaker takes time to clear and the circuit breaker does not remain closed in response to the first closure. The first reclosure is usually made without a delay since operating experience has shown that the majority of faults are of a temporary nature such as lighting flashovers, and will not be reestablished after an interruption of the fault current.
If the circuit breaker does not remain closed after the first reclosure, the relay makes additional reclosures at suitably graded intervals. It is common practice for the reclosing relay to make two additional reclosures. If the circuit breaker does not remain closed after the third reclosure, the reclosing relay goes to a lockout state, and manual action is required to reset the circuit breaker and the reclosing relay.
Conventionally, reclosing relays have been electromechanical devices While these devices are very reliable, they are not very flexible.
It is a primary object of the invention to provide a reclosing relay which can be more easily adapted to varying conditions.
It is also an object of the invention to provide such a reclosing relay which maintains continuity of operation despite interruption in power to the relay.